Bismuth activated gadolinium niobate phosphors

ABSTRACT

COMPOUNDS OF BISMUTH-ACTIVATED GADONLINIUM NIOBATE ARE NOVEL AND USEFUL BLUE-EMITTING PHOSPHORS UNDER CATHODE RAY AND U.V. EXCITATION.

Oct. 23, 1973 GRISAFE ETAL 3,767,589

BISMUTH' ACTIVATED GADOLINIUM NIOBATE PHOSPHORS Filed May 22, 1972NANOMETERS EMlSSlON SPECTRA: 2537' EXCITATION United States Patent OU.s. cum-301.4 R 7 Claims ABSTRACT OF THE DISCLOSURE I Compounds ofbismuth-activated gadolinium niobate are novel and useful blue-emittingphosphors under cathode ray and U.V. excitation.

BACKGROUND OF THE INVENTION This invention relates to syntheticinorganic phosphors. More particularly the invention relates tocompounds of bismuth-activated gadolinium niobate which emit light inthe blue region of the visible spectrum under excitation with suitableradiation such as cathode ray or ultraviolet.

Phosphors are known products of commerce. Generally, the term isemployed in the art to describe luminescent or fiuoroscent solids whichcomprise two essential ingredients: a host matrix and an activator.There are many known host materials including niobates, silicates,phosphates, vanadates, etc. Two known niobate phosphors are yttriumniobate and lanthanum niobate (YNbO, and LaNbO respectively). Thesephosphors are both selfluminescent and activated by bismuth. Of thesetwo, the yttrium niobate bismuth is the brightest; however, it would beadvantageous if a brighter niobate phosphor could be found, as well asone which emitted more in the blue region of the spectrum.

OBJECTS AND SUMMARY OF THE INVENTION Accordingly, it is an object ofthis invention to provide such a phosphor.

This and other objects are accomplished in one aspect of the inventionby the provision of phosphor compounds of bismuth-activated gadoliniumniobate. More particularly, a phosphor having the general formula Gd BiNbO where x 0.2 is provided.

BRIEF DESCRIPTION OF THE DRAWING The single figure depicts the relativebrightness and the color peaks of the phosphor of the invention and aprior art phosphor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the inventionwith greater particularity there are herein described phosphors whosecompositions can be shown by the general formula Gd Bi NbO where 0 x0.2. Such phosphors yield blue luminescence when exposed to cathode raysor ultraviolet radiation of 2537 A. wavelength. The single figurecompares one of the specific phosphors of this invention, namely and aprior art phosphor Y Bi NbO It will be seen from a comparison of thepeaks of the respective phosphors that the gadolinium niobate is 'bothbrighter and bluer; i.e., is shifted more toward the blue end of thevisible spectrum.

It should here be noted that, while as noted above, the yttrium andlanthanum niobate compositions are selfluminescent, gadolinium niobatewithout activation by bismuth is inert under both cathode ray andultraviolet excitation.

ice

The phosphors described herein can be prepared from any startingmaterials which will provide the phosphors with the desired amounts ofthe oxides of gadolinium, bismuth and niobium in the final product. Inheat treating these phosphors, a variety of non-reducing atmospheressuch as oxygen, air, carbon dioxide, etc., can be employed. While thesephosphors can generally be fired in either covered or uncoveredcontainers, when high temperature and/or long periods of time areemployed it is preferable to utilize covered containers to minimize theloss of bismuth due to volatility.

The following examples illustrate without undue limitation theproduction of phosphors according to this invention.

EXAMPLE 1 15.701 g. of gadolinium oxalate hydrate, 6.646 g. Nb O and0.350 g. Bi O are blended in any one of several conventional dry methodsor by a wet method using a volatile inert carrier such as acetone. Themixture is heated between 600 C. and 1650 C. for at least 30 minutes,preferably remixed as above to insure homogeneity and then preferablyrefired between about 1000 C. and 1650 C. in air for at least 30minutes; The firing time and temperature can be varied so long as theyare sufiicient to form the gadolinium niobate compound. The resultingphosphor has as its stoichiometry and luminesces blue under ultraviolet(2537 A.) or cathode ray excitation.

EXAMPLE 2 14.568 g. of gadolinium oxylate hydrate, 6.646 g. 'Nb O and1.165 g. Bi O are mixed as described in Example 1. The mixture is heatedat 600 C. for one hour and then at 1350" C. for several hours (e.g.,three). The resulting phosphor luminesces blue under ultraviolet orcathode ray excitation and has the formula Gd0 9BI EXAMPLE 3 9.854 g. ofgadolinium oxylate hydrate, 4.430 g. optical grade Nb O and 0.039 g. BiO are mixed as described in Example 1. The mixture is fired at 700 C.for one hour, remixed in acetone and refired in a covered crucible atabout 1315 C. for several hours. The resulting phosphor, Gd Bi NbOluminesces blue under ultraviolet or cathode ray excitation.

EXAMPLE 4 Any of the above proportions of materials can be mixed as inExample 1 and fired according to the following schedule: heat themixture at about 600 C. to 800 C. for about one hour, remix and refirebetween about 1000 C. to 1400 C. for several hours with a final firingbetween about 1500 C. to 1650 C. for at least several minutes. Thephosphors produced are substantially identical to those of Examples 1-3respectively, depending on the proportions of the starting materials.

It will be seen from the above that there is herein provided a new andnovel phosphor composition that exhibits wide latitude in formulationand in the manufacturing process.

While there have been shown and described what are at present consideredto be the preferred embodiments of the invention, it will 'be apparentto those skilled in the art that various changes and modifications canbe made herein without departing from the scope of the invention asdefined by the appended claims.

What is claimed is:

1. A phosphor material having the general formula Gd Bi NbO wherein 0 x0.2 and Bi is present in an effective amount to achieve luminescence.

2. The phosphor of claim 1 wherein x is 0.03.

3. The phosphor of claim 1 wherein x is 0.1.

4. The phosphor of claim 1 wherein x is 0.005.

5. The method of making a blue emitting phosphor of the general formulaGd Bi NbO wherein O x 0.2 which comprises the steps of blending togetherto form a mixture of materials which when heated at between 600 C. and1650 C. will yield gadolinium oxide, bismuth oxide and niobium oxide,heating said mixture between 600 C. and 1650 C. for at least 30 minutes;

remixing said mixture; and then retiring said remixed 15 mixture in airat between 1000 C. and about 1315 C. for at least 30 minutes.

6. The method of claim 5 wherein said oxide yielding materials are mixedwith acetone and said fired mixture is remixed with acetone.

7. The method of claim 3 wherein said gadolinium oxide yielding materialis gadolinium oxylate hydrate; said niobium oxide yielding material isNb O and said bismuth oxide yielding material is Bi O References CitedUNITED STATES PATENTS 3,250,722 5/1966 Borchardt 25.230l.4 R 3,427,5662/1969 Hoskins et a1. 252301'.,4 R 3,496,482. 2/1970 Hoskins et al.'-252301.4 R 3,503,006 3/1970 Hoskins et al. 25230l.4 R 3,338,841 8/1967Brixner 252--301.4 R

OTHER REFERENCES Sanatona et al.: Chemical Abstracts, vol. 63, 1965, p.3867c.

OSCAR R. VERTIZ, Primary Examiner 20 J. COOPER, Assistant Examiner 22 3a UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION face: 3,767,589Dated October 23, 1973 Inventor) David A. Grisafe and Carl W. Fritsch,Jr.

I It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Col. 2, line 49 "0005" should be "0.005"

Col. 4, Claim 7, line 1 "3" should be "5" Signed and sealed this 7th dayof May 19714..

(SEAL) Attest:

EDWARD I"I.FLETCHER, JR. 3 I'IARSHALL DANE-I Attesting OfficerCommissioner of Patents

